Well testing and stimulation operations are commonly conducted on oil and gas wells in order to determine production potential and to enhance same if possible. In flow testing a well, a tester valve is lowered into the well on a string of drill pipe above a packer. After the packer is set, the tester valve is opened and closed periodically to determine formation flow, pressure, and rapidity of pressure recovery.
Also generally included in a testing string are a drill pipe tester valve and a circulation valve above the tester valve, the former to permit testing the pressure integrity of the string prior to conducting the test, and the latter to permit the circulation of formation fluids out of the string after the test is completed.
It is desirable, particularly when conducting tests on offshore wells, to employ a testing string which requires a minimum rotation or reciprocation of the drill pipe to operate the tools therein, so as to keep the well blowout preventers closed during the majority of the operation. So-called annulus pressure responsive downhole tools have been developed, which tools operate responsive to pressure changes in annulus between the testing string and the well bore casing. A number of these annulus pressure responsive tools are disclosed in the following patents assigned to the assignee of the present invention. For example, testing valves are disclosed in U.S. Pat. Nos. 3,858,649, 3,856,085, 3,976,136, 3,964,544, 4,144,937, 4,422,506, and 4,429,748. Circulation valves are disclosed in U.S. Pat. Nos. 3,850,250, 3,970,147, 4,113,012, 4,324,293 and 4,355,685. It is also known to operate a tool to take a sample of formation fluid with annulus pressure, as disclosed in U.S. Pat. Nos. RE 29,562 and 4,063,593. Moreover, tools which combine multiple functions have also been developed, as disclosed in the aforesaid RE 29,562 (testing and sampling) and U.S. Pat. Nos. 4,064,937, 4,270,610 and 4,311,197 (circulating and sampling). While many of the aforesaid tools provide a biasing source comprising an inert gas under pressure to oppose annulus pressure, it is also known to employ a compressible fluid, such as silicone oil, as disclosed in U.S. Pat. Nos. 4,109,724, 4,109,725, and U.S. Application Ser. Nos. 354,529 and 417,947. Moreover, the use of a compressed gas in combination with a fluid, such as oil, is disclosed in U.S. Pat. Nos. 4,422,506 and 4,429,748.
There exist other testing, circulating and sampling tools and the like which operate in response to annulus pressure, as disclosed in U.S. Pat. Nos. RE 29,638, 3,796,261, 3,823,773, 3,901,314, 3,986,554 and 4,403,659, assigned to Schlumberger Technology Corporation; U.S. Pat. Nos. 4,105,075 and 4,125,165, assigned to Baker International Corporation; U.S. Pat. No. 4,341,266, assigned to Lynes, Inc.; and U.S. Pat. Nos. 3,891,033 and 4,399,870, assigned to Hughes Tool Company.
Drill pipe tester valves which operate responsive to pipe string manipulation are disclosed in U.S. Pat. Nos. 4,295,361, 4,319,633, 4,319,634 and 4,421,172, all assigned to the assignee of the present invention.
While the tools of the prior art are diverse in design, they suffer from a number of deficiencies in actual operation. First, while several functions have been combined into one tool in some instances, the operation thereof depends upon use of multiple pressures, shearing of pins, or pressure variation both inside and outside the pipe string. Inability to maintain precise pressure levels hampers the use of some of these tools, while the use of shear pins prevents further operation of other tools after the pins have sheared. Many prior art tools employing therein a fluid such as oil utilize fluid metering means such as flow restrictors of a jet type exemplified by the Lee Visco Jet, described in U.S. Pat. No., 3,323,550, in conjunction with check valves. Such metering means and check valves are susceptible to clogging and often fail to operate properly if the fluid becomes contaminated or is of a low quality to begin with, a common occurrence in many remote areas of the world where these tools are operated. In addition, the use of fluid metering means requires an inordinate amount of time to cycle the prior art tools, thus prolonging time on the jobsite and cost to the well operator. Furthermore, temperature increases or decreases in the well bore from ambient surface temperatures change viscosity in the oils employed in these tools, thus affecting the performance of fluid metering means and altering tool cycling time. A further disadvantage resides with those tools utilizing oil, water or other liquids as an expendable fluid, as they are limited in the number of times they can be cycled downhole.
Finally, even though some attempts have been made to combine multiple functions in a single tool, there has heretofore been no successful combination of more than two functions in a single tool.